Many semiconductor devices include circuitry intended to allow external testing equipment to cause testing procedures to occur within the semiconductor devices. External testing equipment may be coupled to a semiconductor device and may transmit and/or receive a variety of signals to and/or from the semiconductor device. Among the possible signals transmitted from the test equipment to the semiconductor device may be a clock signal and a test clock signal, as well as test data input and output signals.
During some testing procedures, it may be advantageous to cause the semiconductor device to operate at a clock frequency that may be approximately the frequency intended for use during normal full-speed operation of the semiconductor device. This may be accomplished by the testing equipment providing a full-speed clock signal to a semiconductor device clock input. The semiconductor device may also receive the test clock signal from the testing equipment at a test clock input. The test clock signal may be a slower frequency clock used to shift test data in and out of the semiconductor device.
Semiconductor device clock frequencies for normal full-speed operating conditions tend to increase over time, and now often exceed one Giga hertz. As these operating frequencies increase, it becomes more difficult and expensive to have test equipment provide full-speed clock signals during testing procedures.